In the fields of electronics technology and optical technology, a variety of elements having patterned coatings have recently come into use. These elements are formed by providing a coating of a substance having a specified physical property, such as an electrically conductive substance, a semi-conductive substance, a non-transparent substance or a substance capable of absorbing light of a specified wavelength region, in a predetermined pattern such as parallel lines, dots, letters, numerical figures and geometrical figures on a substrate such as a glass or plastic sheet. Examples of these elements are electronic circuit elements, display elements, glow modulating filters and diffraction gratings.
Formation of a patterned coating in the production of elements of this kind can be effected by methods which can be roughly divided into the following two groups.
(a) Method which comprises masking a coating adhering to the entire surface of a substrate with a photosensitive resin, and photoetching the coating so as to leave the desired portions in the predetermined pattern and remove the unwanted portions. PA1 (b) Method which comprises masking a substrate surface with a sheet-like masking material having openings in the desired pattern, and directing a film-forming material from a source toward the substrate surface through the mask by vacuum deposition, sputtering, CVD (chemical vapor deposition), solution spraying, etc.
According to method (b), the pattern transferring accuracy is worse than in method (a). But because the process steps can be drastically simplified, method (b) is commercially advantageous. With an increasing demand for the aforesaid elements, method (b) has been considered as promising, and it has been strongly desired to improve the pattern transferring accuracy in this method.
The most important problem in the formation of a patterned coating by using a sheet-like mask (to be referred to simply as a mask) is the degree of adhesion between the mask and the substrate. The most general method of contacting the mask intimately with the substrate is to lay the mask on the substrate, and press the mask against the substrate at its edge portion outside a pattern-forming area by holding and fixing their edges by a holding device. According to this method, the adhesion between the mask and the substrate at the openings near the center of the mask becomes worse as the thickness of the mask becomes smaller and the area of forming the pattern becomes broader. Consequently, a large gap occurs between them. If such a gap exists, particles of the film-forming substance fly to an area which should be masked, and the transferring accuracy of the pattern decreases.
A method was therefore suggested in which in order to increase the adhesion of the mask to the substrate, the mask is urged against the substrate not only at its edge portion but also at its pattern-forming area by a press member composed of a number of elastic wires such as piano wires which are stretched across the mask and in proximity to the patterned openings. When the patterned openings are very close to each other or the pattern is very complicated, meticulous care and much time are required in setting the press member in position completely away from the openings so as not to hamper the formation of a patterned coating on the substrate surface. Such a method is therefore unsuitable for commercial production. Furthermore, contacting of the press member within the pattern-forming area may become impossible depending upon the type of the pattern.
It is an object of this invention to provide a method for forming a patterned coating, which has solved the problems of the prior art and can transfer the pattern on the mask to the surface of the substrate with a high degree of accuracy.
Another object of this invention is to provide a method in which the pattern openings of the mask can be always urged against the substrate during the formation of the coating irrespective of the type of the pattern.